Description:
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Hi,
I executed this piece of code yesterday and have the feeling there may be a problem in how Datetime object parses strings. 
The "new DateTime()" instruction returns a DateTime object with current date. The "new DateTime('yyyy-mm-dd') return a DateTime object with date given. Depending on how you instantiate, interval returned by the diff method will not return same amount of months. 

In code below, if you comment line 2 or not, the m property of DateInterval obkect will not be the same (in one case it is 3, in the other it is 2). 

I have the feeling that these two ways of instantiating a DateTime should process a difference with another the date the same way. 

Am I wrong on this topic?

Thanking you in advance. 

Test script:
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$date1 = new DateTime();
$date1 = new DateTime($date1->format('Y-m-d')); // If commented, not same result in number of months
$threemonthsago = new DateTime('3 months ago');
$diff = $threemonthsago->diff($date1);	
echo 'Number of months: '.($diff->m + 12*$diff->y );echo '<br/>';
echo '$date1 in d-m-Y format: '.$date1->format('d-m-Y');echo '<br/>';
echo '$threemonthsago in d-m-Y format: '. $threemonthsago->format('d-m-Y');

Expected result:
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In the code above, first echo should always be 3 months. 

Actual result:
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In the code above, if second line is commented, it shows 3, otherwise 2.